Ultrasound-Shaken Implants Reveal Hidden Bone Infection Pathogens

When surgeons remove plates, screws, and nails that were once used to hold a broken bone together, they are often looking for answers. Was the fracture healing cleanly, or was a smoldering infection hiding on the metal surface? A new study from Erasmus Medical Center in Rotterdam suggests that a technique borrowed from the world of prosthetic joint surgery can provide those answers far more often than conventional methods alone. By bathing removed fracture-fixation hardware in ultrasound waves and culturing the fluid that shakes loose, researchers found that they could detect bacteria that standard tissue cultures missed, changing both diagnoses and antibiotic decisions in a meaningful share of patients.

The condition at the heart of the research is fracture-related infection, or FRI, one of the most feared complications of operative fracture care. Reported infection rates range from roughly 1 to 2 percent in closed fractures to as high as 29 percent in open fractures, where the bone breaks through the skin and bacteria have a direct route to the implant. Diagnosing FRI is notoriously difficult because symptoms vary widely, and conventional culture methods frequently come back negative or inconclusive. Literature reviewed by the team indicates that between 9 and 22 percent of confirmed fracture-related infections yield no bacterial growth at all on standard cultures, leaving surgeons to treat blindly.

Sonication offers a way around one of the central problems: biofilm. Bacteria on implanted metal do not float freely; they encase themselves in a sticky, protective matrix that clings tenaciously to the implant surface. Tissue samples taken around the hardware may capture only scattered organisms, while the bulk of the microbial population remains locked on the metal itself. Sonication uses high-frequency sound waves, typically delivered in a specialized bath, to generate powerful microscopic forces that dislodge bacteria from the biofilm into a surrounding fluid. That fluid can then be cultured, theoretically revealing the true microbial picture. The approach has already proven its worth in periprosthetic joint infection, where multiple studies have shown higher sensitivity than tissue cultures alone.

In the new study, published in the Journal of Bone and Joint Infection, Anas Zouitni and colleagues analyzed prospectively collected data from patients who underwent partial or complete removal of osteosynthesis implants between July 2012 and May 2021 at their tertiary university hospital. The team aimed to send every removed implant for sonication, regardless of whether infection was suspected. To be included in the analysis, patients needed at least three tissue cultures taken during surgery, each collected with separate sterile instruments and incubated for a full fourteen days on multiple media types, including blood, chocolate, McConkey, and Brucella agars under both aerobic and anaerobic conditions.

The sonication protocol itself was precise. Retrieved hardware was transported to the microbiology laboratory in sterile hard-polypropylene containers and processed within six hours of removal. A sodium chloride solution was added to cover at least 90 percent of the implant, and the container was placed in a sonication bath for one minute at 40 kilohertz, with manual vortexing for 30 seconds before and after. Aliquots of the resulting fluid were plated onto agar media and inoculated into aerobic and anaerobic blood culture bottles, all incubated for fourteen days. Bacterial identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, a rapid technique that fingerprints proteins to identify organisms at the species level.

The researchers classified 96 patients using the international consensus criteria for fracture-related infection established by the AO Foundation and the European Bone and Joint Infection Society. Before sonication results were considered, the cohort contained 14 aseptic cases, 35 suggestive FRI cases, and 47 confirmed FRI cases. After incorporating sonication fluid culture results, four cases moved from aseptic to suggestive FRI, and three cases escalated from suggestive to confirmed FRI. In three additional cases where infection had been confirmed on non-microbiological grounds, sonication was needed together with a single positive tissue culture to achieve full microbiological confirmation. In total, the technique was essential for confirming the diagnosis in about 6 percent of confirmed infections.

The diagnostic performance numbers tell a nuanced story. Tissue cultures alone achieved a sensitivity of 74 percent and a specificity of 98 percent. Sonication fluid cultures on their own were more sensitive, at 84 percent, but less specific, at 83 percent. The real power emerged when the two methods were combined: sensitivity rose significantly from 74 to 88 percent, a difference the authors report as statistically significant. Specificity, however, dropped from 98 to 83 percent with the combination, reflecting the fact that sonication fluid, which requires extra handling steps, is more vulnerable to contamination. The team noted that 33 percent of patients classified as aseptic showed a positive sonication culture, almost all involving low-virulence organisms such as coagulase-negative staphylococci and Cutibacterium acnes, with very low bacterial counts suggesting contamination rather than true infection.

Perhaps the most clinically consequential findings concerned antibiotic therapy. Among 50 confirmed fracture-related infections, sonication results were concordant with tissue cultures in 21 cases, meaning the technique would not have changed management. But in 13 cases, sonication detected an additional virulent pathogen, all Enterococcus species, that tissue cultures had missed, directly influencing the antibiotic regimen. In another set of cases, sonication revealed additional low-virulence pathogens that could have influenced therapy in 8 cases, or 16 percent of the confirmed infections. Taken together, the authors conclude that without sonication, roughly 6 to 16 percent of confirmed FRI cases would have received suboptimal treatment because not all causative pathogens would have been identified.

The study also uncovered factors that predict when sonication will pay off. In patients who had received antibiotics in the one to fourteen days before hardware removal, sonication was positive in 10 of 12 cases while tissue cultures were positive in only 8, reinforcing the idea that sonication retains value when prior antibiotics suppress growth in tissue samples. In regression analysis, implant loosening was associated with nearly fourfold higher odds of a positive sonication result, while non-union was independently associated with lower odds. Most positive sonication cultures occurred in late infections, more than ten weeks after the index surgery, when mature biofilms have had time to establish on the implant surface.

The authors argue that their findings, the first to assess the added diagnostic value of sonication in FRI using prospectively collected data, support routine use of the technique alongside standard tissue cultures, provided that an adequate number of cultures is obtained according to protocol. They note that even when the currently recommended minimum of five tissue cultures is met, as it was in about 36 percent of confirmed cases here, sonication still increased the microbiological yield. They also suggest a practical idea for future study: during debridement and implant retention procedures, exchanging a single screw for sonication culture might enhance pathogen identification without significantly extending surgery. The team recommends validation of these results and consideration of formally incorporating sonication fluid culture into future FRI consensus guidelines, a step that could help surgeons worldwide identify the microbes hiding on the metal and target them with precision.

Subject of Research: Diagnostic value of sonication fluid culture for identifying pathogens in fracture-related infection

Article Title: Sonication fluid cultures enhance pathogen identification in fracture-related-infection (FRI)

Article References: Zouitni, A., Yusuf, E., van Oldenrijk, J., Hagenaars, T., Croughs, P. D., Bos, P. K., Eygendaal, D., & Veltman, E. S. (2026). Sonication fluid cultures enhance pathogen identification in fracture-related-infection (FRI). Journal of Bone and Joint Infection, 11(4), 431-440. https://doi.org/10.5194/jbji-11-431-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-431-2026

Keywords: fracture-related infection, sonication fluid culture, biofilm, osteosynthesis implants, tissue cultures, diagnostic sensitivity, antibiotic therapy, orthopedic surgery, microbiology, MALDI-ToF, implant removal, Erasmus Medical Center